Double ended spring shock absorber

ABSTRACT

Double ended spring shock absorber consisting of a cylinder having pistons reciprocable therethrough at each end and a compressible material disposed between the end plugs within the cylinder.

United States Patent [191 Cope et al.

[451 May 8,1973

[54] DOUBLE ENDED SPRING SHOCK ABSORBER [75] Inventors: Geoffrey WiltonCope, Williamsville; Loren William Smith, Eggertsville, both of N.Y.

[73] Assignee: Dresser Industries, Inc., Dallas, Tex.

[22] Filed: Mar. 18, 1971 [21] Appl. No.: 125,669

[52] U.S. Cl. ..267/65 R [51] Int. Cl ..F 16f5/0O [58] Field of Search..267/65 R, 65 A [56] References Cited UNITED STATES PATENTS Wastenhagenet al ..267/65 R FOREIGN PATENTS OR APPLICATIONS 214,268 4/1924 GreatBritain ..267/65 Primary ExaminerJames B. Marbert Attorney-Robert W.Mayer, Thomas P. Hubbard, .Ir., Daniel Rubin, Raymond T. Majesko, Roy L.Van Winkle, William E. Johnson, Jr. and Eddie E. Scott [57] ABSTRACTDouble ended spring shock absorber consisting of a cylinder havingpistons reciprocable therethrough at each end and a compressiblematerial disposed between the end plugs within the cylinder.

9 Claims, 1 Drawing Figure PATENTEDW 81975 INV4ENTORS: GEOFFREY W. COPENEY DOUBLE ENDED SPRING SHOCK ABSORBER Heretofore, springs, generallyknown as liquid and compressible solid springs, have been suggested forvarious applications where mechanical springs, such as, coil or leafsprings have been used and in applications where mechanical springscould not be used because of their physical limitations. In a liquid orsolid spring, a lightweight piston is accelerated when the spring isactuated, whereas in a mechanical spring, the entire mass of the springis moved to some degree each cycle so that the natural frequency of aliquid or solid spring is much higher than a coil spring, enabling it tobe operated at much higher velocities. A liquid or solid spring is muchmore compact and much smaller than a mechanical spring which will carrythe equivalent load. Conversely, a liquid or solid spring of a givensize will carry many times the load of the same size mechanical spring.

Liquid or solid springs have been used between two relatively moveableparts, the container being connected to one of these parts and thepiston being connected to the other. When a force or load is applied toone of the two relatively moveable parts, the piston is forced inwardlyof the container, compressing the medium within the container. When theforce or load is relieved, the liquid or solid expands returning thepiston, and the part, to which it is connected, to its initial position.

These single ended pistons have been suggested for use in automobileunderframing for cushioning of the bumper; in aircraft landing gear; inartillary gunnery mechanisms; in end-of-car cushioning units for railwaycars; and other environments. The liquid spring units are generallydesigned to accommodate a force against the piston head. The piston headis generally of small diameter with respect to the cylinder diameter;therefore, it offers little resistance to the passage of liquid past it.Certain applications have required the accommodation of a great force orshock causing design and materials problems with single ended springs.It has been suggested to place two single ended liquid springs back toback. However, such a solution presents mechanical problems and reducesthe efficiency of each individual unit along with lost economy.

Accordingly, it is an object of the present invention to provide adouble ended spring shock absorber.

Another object of the invention is to provide a spring shock absorbercontaining a piston at each end thereof which individually travel lessdistance than the piston of a single ended liquid spring of the priorart.

A further object of the invention is to provide a spring shock absorberin which two pistons act against each other within a cylinder through acompressible medium.

In order to more fully understand the nature and scope of the presentinvention, reference should be had to the following detailed descriptionand drawing, the single FIGURE of which is a partial cross sectionalview of a preferred construction for the double ended spring shockabsorber of the present invention.

in accordance with the present invention, there is provided a doubleended spring shock absorber comprising an open ended tubular member. Apiston is disposed and reciprocable within each end of the tubularmember and contains a rod which extends externally thereof. A closureplug is fixedly attached to each end of the tubular member andaccommodates the piston rod which passes therethrough. A compressiblematerial is disposed within and fills the tubular member between theclosure plugs.

Compressible liquids suggested in the prior art are oil, water, alcohol,etc. However, silicone fluids are preferred. Compressible solidmaterials that may be utilized are plastic, such as, a dense and hardsilicone or other materials, such as polystyrene, cellulose acetate,nylon, etc., depending on the loads desired. The spring is preloaded byprecompressing the compressible material when filling the chamber of thecylinder. When a working load is applied to either end of the spring,the material is compressed to absorb the load against the other pistonand returns the loaded piston by increase in volume when the load isrelieved.

A single ended liquid spring, liquid spring shock absorber orcompressible solid spring shock absorber requires a piston rod of acertain length to provide the necessary travel. The column strength ofthe outstanding piston rod is determined by its length, its radius ofgyration, the amount of initial eccentricity and the materialproperties. The further the piston rod stands out from the cylinder thelarger the diameter must be to resist the greater initial eccentricityand the consequently larger buckling loads. Inspection of any of thecolumn formulas will readily show the relationship between the columnlength and the radius of gyration or indirectly piston diameter.

Since the liquid spring shock absorber rate is completely dependent uponthe volume of the piston rod that is introduced into the cylinder duringcompression, it follows that the larger the diameter of the rod thehigher the spring rate and the shorter the allowable travel, orconversely, the larger the piston diameter the greater the volume ofliquid required to provide the required level because of the limitedcompressibility of the liquid (approximately 8 percent). Thus, there isa tie-in between the piston rod length and travel, its diameter and thevolume of the cylinder or container.

The double ended cylinder first of all reduces the outstanding length ofthe piston rod by one-half and thereby permits its diameter to bereduced. The piston rod volume that enters the cylinder for a giventravel is likewise reduced along with the volume of liquid necessary tokeep the compression below the maximum allowable. It provides a means toreduce the size of the cylinder or container and/or the spring rateand/or the pressure gradiant during closure compared to a single endedunit.

One other factor is the hoop strength of the cylinder wall and thereforethe material that can be used. If the pressure can be kept down eitherby use of a smaller diameter piston rod or by a larger volume of liquid,then lower strength materials can be utilized for the cylinder whichusually reflects a lower cost.

Referring to the drawing, there is shown a double ended spring 10according to an embodiment of the invention. It includes a cylinder ortube 12, the wall 14 of which is preferably of substantially uniformdiameter from end to end. The tube operatively supports pistons 16 whichare reciprocable axially thereof and relative thereto.

The opposite initially open ends 18 of the tubular wall 14 are closed bya plug 20. The plug 20 has an end wall 22 and a sidewall 24 thatdecreases in thickness internally of the tubular member. The plug has acentral aperture divergingly tapered toward the inside of the cylinder12. The tapering surface provides a space between a portion of theaperture and a piston rod 28 attached to the pistons 16 for disposing asealing means 30 to prevent loss of the compressible material. As shownin the drawing, the sealing means 30 contains an annular groove 32therein providing two lips 34 and 36 for sealing the piston rod 28 andaperture surface of the closure plug. The outer periphery 24 of theclosure plug contains an annular O-ring 38 embedded therein for sealingthe closure plug against the inner surface of the cylinder. The sealsmay be composed of a plastic yieldable material, such as, Teflon, nylon,Delrin or other materials well known to those skilled in the art. Theclosure plug also contains an annular depression 40 on the internal end42 thereof to provide a flow path for the compressible material.Variations, of course, can be made in the closure plug design and thesealing members. The closure plug is attached to the tubular member bymeans of a threaded portion 46 on the internal surfaces of the tube.However, the closure plug may be secured therein by lock rings, swaging,welding, brazing and the like.

The piston rods contain a terminal head 48 which has a hemisphericalouter surface 50. The spherical surface is preferred for achievingequalization of the piston when in use. The compressible material 52fills the space in the form of a column between the closure plugs ateach end.

While it is preferred that the tubular member be of uniform crosssection, certain applications may require that the cross sections ofeach end of the tube and the accompanying pistons vary, i.e., by gradualtapering. In addition, the design shown in the drawing is particularlyapplicable to compressible liquids. With compressible solids, the pistonwould have to be of slightly smaller diameter to permit extrusion of thesolid past it.

The important aspect of design with respect to the piston diameter andcylinder diameter for spring shock absorbers as contrasted with liquidsprings is that sufficient tolerance between the piston and cylindermust be maintained to permit resistant passage of the compressiblematerial past the piston. Impact forces cause the piston rod 28 and thepiston 16 to move inwardly of the chamber. During such movement, thecompressible solid or liquid 52 is forced through the annular orificesurrounding the piston, thereby producing a throttling effect. Also, asthe piston rod moves inwardly of the chamber, the volume of thecompressible material 52 is reduced thereby increasing the pressuretherein. The described throttling effect and volume-pressure change ofthe compressible material serve to dissipate the energy of impact forcesreceived by the piston rod. When the impact forces are removed, theeffective pressure of the compressible material 52, which is unbalancedon opposite sides of the piston due to the differential in areasthereof, causes the piston and piston rod to return to the positionshown in the drawing. During the return stroke of the piston rod, thecompressible material flows back through the annular orifice surroundingthe piston 48 to fill the space being vacated by the latter.

The drawings show that the pistons are identical in configuration.However, within the scope of this invention, the pistons may vary insize and configuration within the uniform diameter cylinder to develop,for example, a two stage compression curve.

Various other modifications may be made herein without departing fromthe spirit and scope of the present invention.

Having thus described the invention in detail and with sufficientparticularity as to enable those skilled in the art to practice it, whatis desired to have protected by Letters Patent is set forth in thefollowing claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A double ended spring shock absorber comprising an open ended tubularmember, a piston reciprocable through each end of the tubular member andcontaining a rod extending externally thereof, there being an annularoriface between the piston and tubular member, a closure plug fixedlyattached to each end of the tubular member, the piston rod extendingtherethrough, and a compressible material disposed within and fillingthe tubular member between said closure plugs.

2. The spring of claim 1, in which the compressible material isprecompressed within the tubular member to effectively preload thedouble ended spring.

3. The spring of claim 1, in which the compressible material is asilicone fluid.

4. The spring of claim 1, in which a sealing means is provided betweenthe closure plug and the tubular member.

5. The spring of claim 1, in which the closure plug contains an annulardepression internally of the tubular member.

6. The spring of claim 4, in which the sealing means between the rod andclosure plug contains an annular depression internally of the tubularmember.

7. The spring of claim 1, in which the rod extending externally of thecylinder terminates in head having a hemispherical surface.

8. The spring of claim 1, in which the tubular member is ofsubstantially uniform diameter.

9. The spring of claim 1, in which the pistons reciprocable through eachend of the cylinder are of different configuration.

1. A double ended spring shock absorber comprising an open ended tubular member, a piston reciprocable through each end of the tubular member and containing a rod extending externally thereof, there being an annular oriface between the piston and tubular member, a closure plug fixedly attached to each end of the tubular member, the piston rod extending therethrough, and a compressible material disposed within and filling the tubular member between said closure plugs.
 2. The spring of claim 1, in which the compressible material is precompressed within the tubular member to effectively preload the double ended spring.
 3. The spring of claim 1, in which the compressible material is a silicone fluid.
 4. The spring of claim 1, in which a sealing means is provided between the closure plug and the tubular member.
 5. The spring of claim 1, in which the closure plug contains an annular depression internally of the tubular member.
 6. The spring of claim 4, in which the sealing means between the rod and closure plug contains an annular depression internally of the tubular member.
 7. The spring of claim 1, in which the rod extending externally of the cylinder terminates in head having a hemispherical surface.
 8. The spring of claim 1, in which the tubular member is of substantially uniform diameter.
 9. The spring of claim 1, in which the pistons reciprocable through each end of the cylinder are of different configuration. 